Asserting the value of sustainable drainage

Management of water is a major challenge for modern societies — and one that the average person tends to take for granted until they’re knee-deep, or the tap runs dry or dirty. That’s when the mud will fly in the direction of designers, developers, authorities and regulators who haven’t moved towards ensuring sustainable infrastructure and water management. When it comes to reputation, mud tends to stick.

With climate projections predicting more intense and frequent weather events such as floods, droughts and heatwaves, and with regulators and authorities delivering increasing environmental penalties, every development must factor sustainability and resilience into its water and drainage design or face increasing costs.

Over recent decades, knowledge of sustainable drainage systems (SuDS) or water-sensitive urban design (WSUD) methods and techniques has matured, and many examples around the world have demonstrated great success and benefits for the environment and communities. These environmental and social benefits are very real, and are certainly valued by communities and regulators, but they can be hard to quantify in monetary terms except by considering the costs of remediating the alternative scenarios, such as dealing with pollution or cleaning up flood damage.

For designers and developers, the slow rate of adoption of sustainable solutions is likely due to a combination of factors, including preferences for the familiar, a perception of higher costs of construction compared to traditional approaches, and a lack of comprehensive understanding of interactions in a wider catchment.

The good news is that sustainable drainage features can be easily integrated into urban development without undue excess cost. Even at a very small scale, sustainable drainage can provide significant benefits in terms of water quantity, water quality, amenity and biodiversity.

Defining sustainable urban drainage solutions

In essence, sustainable drainage is about coping with the quantity of water (such as how to handle large volumes of rainfall and stormwater to avoid flooding) as well as preserving or improving the quality of water (such as by filtering pollutants and contaminants out of stormwater before it returns to waterways).

Urban development replaces natural ‘soft’ surfaces with artificial and non-absorbent ‘hard’ surfaces. This means that rainfall and run-off can no longer soak into the ground and instead need to be captured and transferred away. Traditional drainage systems do little to prevent the run-off mixing with sediment and other pollutants, so adequate water treatment is needed for urban run-off, and that comes at significant cost.

Sustainable drainage alternatives allow integration of more ‘soft’ surfaces which can act as sponges and filters. This restores some of the natural elements of the water cycle. Water is able to be stored or slowed, which helps prevent flooding and promotes absorption. The permeable surfaces and vegetation also provide a series of simple treatment stages to maintain or improve water quality, including filtration, insect and microbial activities, and UV radiation.

Sustainable road drainage involves greater use of swales and permeable paving, alone or in combination. For buildings, sustainable drainage practices move beyond the traditional methods of diverting water from roofs and driveways into the underground stormwater system, and embrace features such as green roofs and rain gardens which reduce the speed and quantity of run-off and provide natural filtration for better water quality. Swales can be combined with these features to collect the drainage from individual buildings.

Many of these features can be integrated into developments at comparable construction and maintenance costs to traditional approaches.

Counting the benefits

By increasing vegetation, sustainable drainage approaches not only ensure better water filtration and water retention, they also promote groundwater recharge by slowing the water flow and allowing percolation into the underground strata. More vegetation also means a greener urban environment, with habitats for plant, animal and insect life, space for recreation, and a more pleasant and appealing landscape for human habitation. Green roofs combine these biodiversity and amenity benefits, as well as helping to regulate building temperatures by insulating during the winter and absorbing heat during the summer.

But what does this mean to a developer in monetary terms, or in the short term? Can these amenity and environmental benefits be advantageous to the bottom line?

For developers, it is possible that development footprints could potentially be extended by counting elements such as green roofs, rain gardens, swales and permeable paving as significant portions of a development’s requirements for open-space amenity as well as flood storage. Development levies from local and regional authorities could be reduced if those authorities were to benefit from the reduced costs of water treatment and flood remediation. Strong environmental credentials for both developers and developments will appeal to increasingly socially and environmentally conscious consumers.

Driving the agenda

For these benefits to be realised, everyone must do their part to understand and increasingly apply sustainable drainage approaches. In some jurisdictions, more widespread implementation could be driven by support and direction from governing bodies to embed sustainable approaches into mandatory requirements. Similarly, local and regional authorities can move the agenda forward with the development of catchment-wide sustainable drainage master plans and quantification of the cost-effectiveness of these plans. An incentive program that returns cost savings to developers who incorporate sustainable drainage features is another opportunity to promote change.

Designers who begin to allow for integration of sustainable drainage features at the earliest stages of design, without increasing construction costs or significantly impacting on the density of the development, will further demonstrate the advantages of sustainable approaches.

Exploring our options in the face of changing climate conditions is the responsible choice. Taking the time to understand and promote the benefits of sustainable drainage solutions and educate others about those benefits is a first step. Once everyone involved in regulation, planning, design, construction and property development fully recognises the ongoing benefits, we are far more likely to see wider incorporation of sustainable drainage and the greening and softening of our concrete jungles. It won’t be very long before our communities simply expect it.

*Andrew Harrison is Golder’s Design Group Leader for South Australia and Victoria. Managing a team of 40 engineers and CADD technicians with significant experience in the design and construction supervision of sediment and surface water management infrastructure, Andrew is a Chartered Professional Engineer (Civil, Environmental and Leadership & Management) and a Project Management Professional with 20 years’ experience in water, tailings and waste management projects in Australia, Africa, Southeast Asia, the United Kingdom and Ireland. Andrew also has presented on the topic of sustainable drainage at the 10th International Water Sensitive Urban Design Conference and the 9th International Urban Design Conference.

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